Microstructure, phase equilibria and properties of Cr-Si

The present paper describes phase equilibria, microstructure and properties of directionally solidified Cr-Si, and V-Si binary alloys with melting temperatures above 1,700C. Attention will be focused on eutectic compositions since directional solidification of eutectics can be used to generate aligned composite microstructures. The concept of directional solidification of eutectics has previously been applied to lower melting temperature systems such as NiTaC and CoTaC alloys. In the present study, crystals of Cr-Cr3Si, and V-V3Si binary eutectic alloys were prepared using cold crucible direction solidification. Growth rates in the range 8 - 250 x 10-3 mms-1 were used, depending on the composition and the desired structure. A range of directionally solidified microstructures from lamellar to rod have been generated. Eutectic phase equilibria are discussed using available phase diagrams, as well as microstructural and chemical analyses. Transmission electron microscopy was used to characterize the orientation relationships between the individual phases of the eutectics. Room temperature and elevated temperature fracture toughness are also discussed